Melting profile

Illustration of the melting process

** Red curve: The red curve represents the solid bed width. The curve starts at the location of the melt vortex formation with a value of 1. This means that the solid bed occupies 100% of the channel width at the start of the melting process. The solid bed width can increase as part of a compression zone or another reduction of the channel cross-section (start of a barrier zone, change to a 2-start screw zone, reduction of the channel gradient). If the melting model changes to disperse melting (e.g. due to a shearing or mixing section), the solid bed width curve ends here. * ** Blue curve: The blue curve represents the melt fraction. In contrast to the solid bed width, the melt fraction can only increase. If the melt proportion reaches the value 1 (=100 %), the entire plastic has melted. When switching to disperse melting, the melting speed can increase or slow down depending on the circumstances.

Solid bed width (red curve): In principle, a high solids bed width is advantageous for the melting rate. However, the solids bed width must not exceed the value of 1, as this would mean that only solids are present in the channel. In this case, the excess solids will first change into the melt channel within a barrier zone. If the solids content in the melt channel also reaches the value 1 or the solids bed width reaches the value 1 outside a barrier zone, the melting calculation is cancelled.
Melt fraction (blue curve): The melting end should be in good time before the end of the screw so that thermal homogenisation can take place within the remaining screw length. The curve shows which zone has what effect on the melting process.
In degassing extruders, the melting end should be before the degassing.